<!DOCTYPE html>
<html lang="zh_CN">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script type="text/javascript">
    var string = 'this is a test case';

    var reg = /\b[a-z]+\b/ig; // \b 是代表是单词的边界（1. 行首 2. 行尾 3. 空格）

    console.log(string.match(reg));

</script>

</html>
